The only thing that could compete with a moving billboard is a REAL billboard of course!  C'mon, you know that billboard you drive past everyday and can quote every word on it, including the phone number or website.  That's exactly what they are meant to do.  The most exciting thing is that for as big as they are, billboards are extremely economic.  Just for fun call and get a price on one today.  You'll have you business on a billboard in no time.